The present technology relates to a method and apparatus for measuring the signal skew associated with each distinct signal path connecting a device under test (DUT), such as an integrated circuit or other electronic device, and associated tester equipment to a time measurement device, such as a time interval analyzer.
In general, an integrated circuit refers to an electrical circuit contained on a single monolithic chip containing active and passive circuit elements. As should be well understood in this art, integrated circuits are fabricated by diffusing and depositing successive layers of various materials in a pre-selected pattern on a substrate thereby imprinting a complex of electronic components and their interconnections. Materials used to manufacturer integrated circuits can include semiconductive materials such as silicon, conductive materials such as metals, and low dielectric materials such as silicon dioxide. The semiconductive materials contained in integrated circuit chips are used to form many basic electronic circuit elements, such as resistors, capacitors, diodes, and transistors.
The complexity of integrated circuits ranges from simple logic gates and memory units to large arrays capable of complete video, audio and print data processing. Integrated circuits are used in great quantities in electronic devices such as digital computers because of their small size, low power consumption and high reliability. The demand for faster and more efficient integrated circuits, however, has created various problems for circuit manufacturers. No manufacturing process is perfect and manufacturing imperfections in an integrated circuit may cause timing irregularities such as pulse-width deviation errors, to name only one type. As signal frequencies increase, the significance of any timing irregularities within integrated circuits also typically increases. By measuring certain characteristics of signal inputs and outputs of an integrated circuit, timing issues that may be present within the integrated circuit can be detected. Such information can then be used to assist integrated circuit manufacturers in developing improved integrated circuits or for detecting defects in mass-produced circuits.
In response to the needs for testing performance measures of integrated circuits and other electronic devices, specialized test systems have been developed to test the functional capabilities and reliability of such products. These test systems and associated components are generally referred to as “Automated Testing Equipment”, and come in a variety of forms. Conventional ATE systems are not always capable of providing comprehensive measurements of integrated circuit I/O signals when such circuits operate at increasingly higher frequencies, such as those on an order of about 10 MHz–1 GHz or higher. As such, specialized time measurement devices have been more recently developed for measuring aspects of such higher frequency signals. An example of such a time measurement device corresponds to a time interval analyzer such as that disclosed in U.S. Pat. No. 6,091,671 (Kattan). Such a time measurement device is capable of making measurements relating to the time period between two or more input signal events where a “signal event” is generally defined as the specific instant in time at which an input signal reaches a certain predefined level. In addition, such a time measurement device is capable of measuring other time characterizations of a signal, such as rise time, fall time, pulse-width, period, frequency, duty cycle, time interval error and other characteristics that may reflect timing errors or frequency fluctuation in a signal.
Another important signal characteristic that is in need of measurement and qualification is the level of synchronization between two or more signals. Lack of such synchronization between signals is called skew. Skew is defined as time differences between similar events on two or more separate distinct signals where ideally there would be no time difference. Skew can be measured between an input and an output signal, between multiple input signals, or between multiple output signals. For example, a DUT is often driven by signals supplied by a test system. Such signals are typically generated by the test system and introduced to the DUT through cables, connects and/or other methods. It is frequently desirable to measure the skew between multiple input signals provided to a DUT by such a test system, and thus a need exists for measuring such skew and relating it to calibration needs of a test system.